MORPHOLOGICAL PART. 123 
of the tegmen at no time attained the rigidity and large size of that in 
the Camerata, nor did those of the dorsal cup, with the exception of 
the anal plates, undergo any material alterations. It was the ventral sac 
which gave to this group its characteristic feature. The sac in the earliest 
forms was quite small, but it soon attained such enormous dimensions that 
already in the Silurian it constituted the greater part of the calyx. At the 
close of the Carboniferous, however, it dwindled down almost as rapidly to 
its former insignificance, so that it is represented in Cromyocrinus, Eupachy- 
crinus, Erisocrinus, and Enerinus by a very short cone. The respiration of 
the Fistulata was apparently directly through the test, but only at the 
posterior side of the calyx. It took place either by means of pores along the 
sac, or by a madreporite placed in front of the sac. The respiratory pores 
of the Fistulata only pierce the edges of the plates; while the water pores of 
recent Crinoids pass through the whole plate. The mode of respiration of 
the Larviformia is unknown. They had apparently no openings in the 
calyx except the anus, but they possessed pores along the arms at the sides of 
the covering pieces, which may have served respiratory purposes. 
Most of the Ichthyocrinide have interbrachial plates, which in some 
species are large and massive, in others small; and some are regularly 
arranged, others irregularly. The mouth is opened out, the ambulacra are 
tegminal, and rest in an integument of very small, ill-formed pieces,* which 
extend to the interradial plates in the cup, and those at the sides of the 
brachial appendages. The small plates form pouches or sacs, which some- 
times reach to the second or third bifurcation. The median lines of these 
pouches are occupied by the ambulacra, which converge to the mouth, sepa- 
rating the orals. 
Here we have among Paleozoic Crinoids a tegmen, which has all the 
characteristics of the disk of living species, down to an uncovered mouth and 
open food grooves, thus demonstrating conclusively that the disk as a ventral 
structure is not confined to the Neocrinoidea. The discovery of this fact led 
to entirely new ideas touching the derivation of these groups. Before, it 
had been supposed that the “ vault’ ceased to exist in Neozoic times, or was 
reduced to the orals. It may now, we feel assured, be considered as estab- 
lished that the structure of the tegmen in the oldest Paleozoic Crinoids, 
* We carefully removed the arms in several well preserved specimens of Onychocrinus Ulrichi and 
O. diversus, and in several instances found portions of the ventral disk imbedded in the dorsal cup, lying upon 
the inner floor of the plates. The disk of these species must have been extremely pliable, and probably con- 
sisted in part of soft tissues. 
